Cancers of blood coopt normal hematopoietic differentiation pathways to create tumor cells. Plant Homeodomain Finger 6 (PHF6) is a tumor suppressor of unknown function in blood malignancies such as T cell Acute Lymphoblastic Leukemia (T-ALL) and Acute Myeloid leukemia (AML). PHF6 contains two zinc finger-like PH domains and localizes to the nucleus where it may play a role in chromatin remodeling. PHF6 is expressed broadly with notably higher expression in lymphoid cells. The goal of this proposal is to understand the function of the leukemia tumor suppressor PHF6, beginning with its role in hematopoiesis. Zebrafish will be used to study hematopoiesis due to the remarkable conservation of molecular pathways that regulate blood development, genetic tractability, and ability to observe embryonic development over a short window of time. My central hypothesis posits that loss of PHF6 will cause an expansion of blood cell progenitors, similar to the overproliferation of lymphocytes observed in leukemias with PHF6 mutations. Aim 1 will determine how phf6 affects the development of blood cell types by first identifying which blood cells express phf6 and then assessing the effect of loss of phf6 on blood progenitor specification. For this work, phf6 expression was knocked down by morpholino and knocked out in mutants generated by TALEN designer nucleases. Aim 2 will identify the molecular mechanisms downstream of phf6 that are responsible for eliciting its effects on hematopoiesis. To find pathways not previously implicated in hematopoiesis as well as place phf6 within established hematopoietic pathways, the pattern of differential gene expression in phf6 mutants will be revealed by RNASeq. This characterization of phf6 function in zebrafish hematopoiesis will be the first in vivo study of phf6 function, as there are no animal models to date. The result of this work will provide powerful insights into the role of PHF6 in human hematological disease, potentially providing drug targets for therapies in the future.